When acquiring an X-ray image, an object to be examined, e.g. a patient, is arranged between an X-ray generating device and an X-ray detector. X-ray radiation emanating from the X-ray generating device is penetrating the object to be examined, subsequently arriving at the X-ray detector. The object to be examined, situated in the path of the X-ray radiation is spatially attenuating the X-ray beam, depending on the specific tissue structure within the object. The X-ray detector is subsequently detecting the spatially attenuated X-ray radiation by determining an intensity distribution of the X-ray radiation, which image information is employed for generating, further processing, and subsequently displaying an X-ray image of the object to be examined.
However, an object to be examined may provide only minor differences when attenuating the X-ray radiation, resulting in a relatively uniformly attenuated X-ray image having low contrast, thus lacking detail of the imaged inner structure of the object.
While certain objects or regions within an object may comprise similar attenuation properties, a phase of X-ray radiation penetrating the object may be influenced to a larger extent by the structure of the object.
In phase-contrast imaging, at least partly coherent X-ray radiation is employed, e.g., generated by a source grating arranged adjacent to, in the vicinity of an X-ray source, e.g. an X-ray tube. Coherent X-rays penetrating the object may allow for subsequent retrieval of phase information.
However, a phase of a wave cannot be measured directly, rather a phase-shift may be required to be converted to an intensity modulation, e.g., by interfering two or more waves. For generating an according interference pattern, a so-called phase grating is employed, arranged between the object to be examined and an X-ray detector. However, an interference pattern generated by only employing a phase grating may be too small to be detectable with a current X-ray detector, due to a lack of spatial resolution of the X-ray detector.
Thus, a further analyzer grating may be employed arranged between the phase grating and the X-ray detector, subsequently providing an interference pattern, which is large enough to be detectable by current X-ray detectors.
Employing such gratings, in addition to the generation of differential phase-contrast image data, the generation of image data deriving from de-coherent X-ray scatter is enabled, the latter type of imaging also being referred to as “dark-field imaging”.
WO 2012/029005 A1 discloses an apparatus for phase-contrast imaging comprising an X-ray source, a first grating element, a second grating element and an X-ray detector element comprising a plurality of detector pixel elements. An object to be imagined is arrangeable between the X-ray source and the X-ray detector element. The first grating element as well as the second grating element is arrangeable between the X-ray source and the X-ray detector element. The X-ray source, the first grating element, the second grating element and the X-ray detector are operatively coupled for acquisition of a phase-contrast image of the object.
However, such imaging device can be still improved, in particular in view of an imaging device, in which the differential phase-contrast imaging can be easily switched on and off.